Experimental Investigation on Microscopic Residual Oil Distribution During CO2 Huff-and-Puff Process in Tight Oil Reservoirs

Kun Qian,Shenglai Yang,Hongen Dou,Lu Wang,Yu Huang,Qian Wang

doi:10.3390/en11102843

Abstract

The determination of microscopic residual oil distribution is beneficial for exploiting reservoirs to their maximum potential. In order to investigate microscopic residual oil during the carbon dioxide (CO2) huff-and-puff process in tight oil reservoirs, several CO2 huff-and-puff tests with tight sandstone cores were conducted at various conditions. Then, nuclear magnetic resonance (NMR) was used to determine the microscopic residual oil distribution of the cores. The experiments showed that the oil recovery factor increased from 27.22% to 52.56% when injection pressure increased from 5 MPa to 13 MPa. The oil recovery was unable to be substantially enhanced as the injection pressure further increased beyond the minimum miscible pressure. The lower limit of pore distribution where the oil was recoverable corresponded to relaxation times of 2.68 ms, 1.29 ms, and 0.74 ms at an injection pressure of 5 MPa, 11 MPa, and 16 MPa, respectively. Longer soaking time also increased the lower limit of the oil-recoverable pore distribution. However, more cycles had no obvious effect on expanding the interval of oil-recoverable pore distribution. Therefore, higher injection pressure and longer soaking time convert the residual oil in smaller and blind pores into recoverable oil. This investigation provides some technical ideas for oilfields in design development programs for optimizing the production parameters during the CO2 huff-and-puff process.

Highlights

The contribution of tight oil is becoming increasingly important for maximizing oil production around the world. [1,2,3,4]
The CO2 injection technique can be generally categorized into CO2 huff-and-puff and CO2 flooding processes
This study provides an interpretation of the CO2 huff-and-puff process from a microscopic perspective as well as suggestions for optimizing production parameters in tight formations

Summary

Introduction

The contribution of tight oil is becoming increasingly important for maximizing oil production around the world. [1,2,3,4]. The contribution of tight oil is becoming increasingly important for maximizing oil production around the world. Due to poor water injectivity, conventional water flooding is unsuitable after natural depletion of tight oil reservoirs. Injection is a reliable method to enhance oil recovery in tight oil reservoirs [5,6]. The CO2 injection technique can be generally categorized into CO2 huff-and-puff and CO2 flooding processes. Due to ultra-low permeability, it is difficult for the gas to drive oil from the injection well to the production well [7]. Tight oil reservoirs often have natural fractures or hydraulic fractures, which result in early break-through during the CO2 flooding process, resulting in very low sweep efficiency [8,9]

Methods

Results

Conclusion